Method and apparatus to estimate relative base station and subscriber terminal locations and using it to increase frequency reuse

ABSTRACT

Method for estimating position information of base stations as well as terminals for three dimensional centralized real-time spectrum management to achieve high spectral efficiency. In one aspect of the invention, the method comprises i) understanding the position information of plurality of base stations, wherein the plurality of terminals and the base stations form a wireless network, ii) determining, at the central controller, position of a terminal via plurality of communication wirelessly between the base stations and a terminal and between the base station and the central controller, iii) applying network wide real time knowledge at the central controller to electronically steerable antennas to use a resource in a different direction then where it is used by other base stations to achieve frequency reuse of one.

STATEMENT OF RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/644,136, now U.S. Pat. No. 7,738,875, entitled “Method and Apparatusto Estimate Relative Base Station and Subscriber Terminal Locations andUsing it to Increase Frequency Reuse”, filed in the United States Patentand Trademark Office on Dec. 22, 2006, which claims the benefit to U.S.Provisional Application No. 60/753,452, filed in the United StatesPatent and Trademark Office on Dec. 22, 2005. The teachings of allpatents, published applications, and references cited herein areincorporated by reference in their entirety herein.

SUMMARY OF THE INVENTION

In this invention, a method is proposed to find relative location offixed base stations in the network; only distance information betweensome subscriber terminals and base stations are known if it is withinthe range. One part of the embodiment proposes a method to localize basestations. The method localizes base stations by selecting a base stationas an origin of a local coordinate, and estimating possible positions ofthe base stations based on distance estimates reported by the terminals.Another embodiment of this invention proposes a method to locateterminals along with base stations. Final embodiment of this inventionproposes a scheduling method in an OFDMA/TDMA/FDMA network in whichthere is a single channel which is used by all base stations. Thescheduling method implements a scheduler in the base station toelectronically steer the antennas of the base stations. Method achievesfrequency reuse close to 1 by using a resource in a direction that doesnot conflict with others by the help of electronically steerableantennas and position information of the base stations and terminals.Further, the scheduler schedules a resource with respect to terminalsbandwidth and informs other base stations not to schedule any resourcein a contending direction. Furthermore, the scheduling methodsynchronizes all the base stations to transmit and receive frames in thesame time and same frequency, whereby each of the base stations is awareof the scheduling in a neighboring base station in a way to reduceinterference.

In another aspect, an apparatus for estimating a relative position of abase station and a terminal in a wireless network and using the relativeposition information to increase frequency reuse is disclosed. Theapparatus includes a central controller, a plurality of terminals, atleast three base stations, and the central controller is communicativelycoupled with each terminal and base station in the wireless networkusing an OFDMA protocol. The terminals on entry into the wirelessnetwork estimate distance information by transmitting digital signals tothe base stations using timing signals or power dissipation. Further,the central controller processes relative location information of basestations and terminals based on distance information transmitted by theterminals. Furthermore, the central controller includes means forcoordinating a scheduler to increase the frequency of reuse by the basestation and the terminals with electronically steerable antenna.

The method and system proposed in this invention can be generalized tothree dimensional space in which base stations and terminals are placedin 3-D space.

BRIEF DESCRIPTION OF DRAWINGS

The objective of the present invention will be more apparent from thefollowing detailed drawings, in which:

FIG. 1 illustrates the network diagram where there are mobile stations,base stations a central controller connected to IP backbone.

FIG. 2 depicts a scanning procedure where each mobile station range witha BS and estimate the distance from the ranging parameters.

FIG. 3 shows the diagram of the method.

FIG. 4 shows the BS locationing with full distance information from MS.

FIG. 5 illustrates a network deployment with three base stations and 19terminals.

FIG. 6 illustrates a build-up mechanism to construct a map from partialinformation.

FIG. 7 illustrates the mechanism to locate the mobile stations.

FIG. 8 illustrates the shadow point if there are only two distanceestimates.

FIG. 9 illustrates the coordination of the central controller to providelocation based scheduling with steerable antennas to increase thefrequency reuse.

INTRODUCTION TO CERTAIN INVENTIVE PARTS OF INVENTION

We consider a wireless network where there are plurality of terminals(Ts) and plurality of base stations (BSs) and central controller as seenin FIG. 1. Terminals can be mobile or fixed but base stations are fixed.We also consider a central controller that can do command control toBSs. A terminal in order to associate with a BS can scan multiple BSs ata given time without initiating an association in a typical networkshown below.

A T first scans for the BS in the network entry procedure. In thescanning procedure the T can estimate its distance to a BS. As a result,after the network entry procedure a T has a set of distance estimatesfor the BSs that are in the vicinity of its range. Distance estimatescan be done in various ways including RSSI based estimation, time offlight based estimation. FIG. 2 illustrates the network for scanning.This scanning report is sent to the central controller.

Based on the collected measurements, the central controller canconstruct the matrix (C) in Table I. Useful information in C is Dmatrix. One can see that there is no mechanism to estimate the distancesbetween BSs and the distances between Ts and some distance estimates arecensored between Ts and BSs because of the range limitations.

TABLE 1 Connectivity Matrix

Methodology for the Invention

For simplicity, we describe two-dimensional localization. However, ouralgorithm extends straightforwardly to three dimensions. We define acluster as a set of four or more BSs, and a set of Ts such each Ts isconnected to at least two of these BSs. A Ts is connected to a BS whenit is in its communication range.

The algorithm can be broken down into three main phases. The first phaselocalizes the elements of clusters, BSs and Ts, into a local coordinatesystem. The second phase finds the relative positions among clusters andcomputes coordinate transformations between each cluster's localcoordinate systems and generates a unique global coordinate system. Thethird phase refines the localization of the clusters using theperiodical updates sent by, the Ts. An example is depicted in FIG. 3.

The three phases of the algorithm are as follows:

Phase I. Cluster Localization: A BS becomes the origin of the localcoordinate system of a cluster and the algorithm estimates the relativelocation of the neighboring BSs which can be unambiguously localized. Wecall this process cluster localization. For each cluster, we identifythe sets of possible positions of the BSs given the distance estimatesreported by the Ts. The Ts and BSs's positions are jointly estimated.The figure below exemplifies the cluster localization for three basestations and five terminals.

Phase II. Cluster Transformation. The algorithm finds the set of BSs incommon between two clusters. In the next step, the remaining BSsbelonging to the two clusters are localized relative to the knownpositions using trilateration. Finally, the algorithm computestransformations between the local coordinate systems of neighboringclusters.

Phase III. Cluster Optimization. Refine the position estimates for eachcluster using the periodical updates sent by Ts. This phase reduces andany accumulated error that results from the incremental approach used inthe second phase.

Cluster Localization

The goal of cluster localization is to compute the position of a clusterof BSs and Ts in a local coordinate system up to a global rotation andpossible reflection. The algorithm provides that the relative positionsof the nodes in a cluster are unique up to a global rotation,translation, and reflection. Using this property any two clusterssharing three BSs form a larger cluster that is also globally rigid. Byinduction, any number of clusters chained in this manner forms aglobally rigid graph.

The algorithm for Phase I, cluster localization, is as follows:

1. The central controller identifies a cluster of nc (nc>4) BSs. GivenD, all the distance estimates dij involving to BSs in the cluster areselected. Let mc (<m) be the number of Ts connected to the mc BSs. Thiscorresponds to performing rows and columns operations on D in order tofind all the submatrices Dc of dimension mc×nc whose elements are notall different form zero. For simplicity, Ts with only one connectivityare neglected.

2. We define a relative coordinate system for the cluster, where BS1 isat the origin and MS1 is arbitrarily placed at location (Dcl 1,0).

3. Localizing BSs in clusters: the relative positions of the BSs in eachcluster are estimated using uniquely the distance estimates in Dc.Algorithm 1 accomplishes this task. We define estMS_(j) as the set ofpossible locations for MS_(j), j=1, 2, . . . , mc that are consistentwith Dc. Similarly, define estBS_(i) as the set of possible locationsfor BS_(i), i=1, 2, . . . , nc that are consistent with Dc. Algorithm 1proceeds by progressively excluding from these sets points that are notconsistent with the matrix Dc.

ALGORITHM 1 Localization within a cluster set estBS _(l) =[0,0] andestMS _(l) =[Dc11,0]; for all MS _(j), j=2, ...mc If Dc _(j0) not ‘full’estMS _(j) = circle([0,0], Dc _(j0)) j=2,...,mc estBS _(i) = circle([Dc₁₁ ,0],Dc _(li)) i=2,...,nc for all BS _(i) delete ( x,y) in estBS _(i)inside circle([0,0], mindistBS ) for all MS _(j) such that Dc _(jl) andDc _(ji)not ‘null’ delete ( x,y) in estBS _(i)outside circle([0,0], Dc_(jl) +Dc _(ji)) while localization iss complete for all BS j for all MSi delete points in estBSj and estMSi not consistent with Dc

When the connectivity is high enough, the relative positions of the BSsare unique up to a global rotation, translation and reflection.

FIG. 4 shows an example of cluster with four BSs and twenty MSs. Thedotted lines show the connections between BSs and MSs. FIG. 5 shows theoutput of Algorithm 1 when applied to this cluster. For simplicity, therelative location of the BSs are rotated and translated such that thealgorithm's output can be compared with the original network.

Cluster Transformation

In Phase II, the algorithm localizes the relative positions amongclusters by chaining together clusters as seen in FIG. 6. Whenever twoclusters have three nodes in common, it is possible to localize theclusters relative to each other. If the first cluster is fullylocalized, we can localize the second cluster by trilaterating from thethree known positions. The global network can be thought as a graph ofclusters, and localization amounts to trilaterating overlapping graphs.This operation can be performed in linear-time.

Cluster Optimization

Distance updates periodically sent by Ts can be used to improve thelocalization performance of the previous two phases. As time goes on,the distance estimates for each graph increase. The central controllercan store all the updates in a database, and Phase I and Phase II can beperiodically re-computed with the updated information. Since the basestation locations are fixed the computed output shall be fed as an inputto do fine tuning.

Terminal Localization

Once the base station locations are fixed, then terminal's position canbe found by triangulation. Terminals that have at least three estimateshave enough information to find the location. FIG. 7 shows the examplesof triangulation.

However, for terminal 2 in FIG. 7, there could be a shadow point as seenin FIG. 8. Location A and B cannot be differentiated by distanceestimates but wireless signal conditions in a given area can be used todifferentiate those two locations, also possibility of having thoseshadow points diminishes with the dense deployment of base stations.Mobility pattern of the terminal also brings side information toidentify its location.

Frequency Reuse with Steerable Antenna Along with Locationing

In OFDMA/TDMA network, interference region between base stations can beavoidable by defining non-overlapping regions inside the given resource.A resource is considered as a collection of slots which are mapped intofrequency and symbol axis. Non-overlapping regions can be constructed inthe central controller via global knowledge of the topology to beassigned to different base stations which are sharing a terminal whichis in the interference region of theirs. In this way, same resource canbe used across the network by all base stations but they do use or blankout some regions according to the occupancy in their interferenceregions. In this way frequency reuse is close to unity.

When an electronically steerable antenna is available along with thelocationing information of each terminal, frequency reuse of unity isachieved via single channel across network by directing non-overlappingresources to different terminals. If there is a conflicting node whichis in the vicinity of BS1 and BS2. If BS1 uses a resource for thatconflicting node, BS2 is allowed to use that resource only in a locationdifferent than the location of that conflicting node consequently whichguarantees no interference with BS1's transmission. As a result, allresources are put to use but they are used with respect to geographicallocation of terminals.

An example is shown in FIG. 9 where there are two base stations; Basestation 1 assigns resource R 1 to terminal 1 and base station 2 uses R 1in different direction which is guaranteed to be

The description presented above only includes some but not allembodiments of the invention. Related other ways of managing threedimensional spectrum management to achieve high spectral efficiency maybe devised without departing from the original scope of this invention,and are thus include by the present invention.

1. A method for finding locations of base stations and using locationinformation of the base stations to increase frequency reuse in awireless network, the method comprising: periodically scanning aplurality of terminals by each of the base stations on entry of theplurality of terminals into the wireless network by ways of transmittingdigital signals from the base stations to the plurality of terminals;estimating respective distances from the plurality of terminals by eachof the base stations using the transmitted digital signals; transmittingdistance information, by at least one of the plurality of terminals,including the estimated distances to each of the base stations; storingand processing the distance information by each of the base stations;determining relative locations of the plurality of terminals withrespect to the base stations using the stored and processed distanceinformation; and electronically steering respective antennas of the basestations based on the determined relative locations of the plurality ofterminals and the base stations to increase frequency reuse by ascheduler in each of at least one base station of the base stations. 2.The method of claim 1, wherein determining relative locations of theplurality of terminals with respect to the base stations includescluster localizing, cluster transforming, and cluster optimizing.
 3. Themethod of claim 2, wherein the cluster localizing includes selecting abase station of the base stations as an origin of a local coordinate,and estimating possible positions of the plurality of terminals based onthe estimated distances.
 4. The method of claim 2, further comprisingusing a smart scheduling at the base stations to increase frequencyreuse.
 5. The method of claim 2, wherein the scheduler schedules aresource with respect to terminals bandwidth.
 6. The method of claim 5,wherein the base stations are synchronized to transmit and receiveframes in the same time and same frequency, whereby the other basestations are aware of the scheduling in a neighboring base station in away to reduce interference.
 7. The method of claim 5, wherein the basestations are synchronized to transmit and receive frames in differenttime and same frequency, whereby the other base stations are aware ofthe scheduling in a neighboring base station in a way to reduceinterference.
 8. The method of claim 5, wherein the base stations aresynchronized to transmit and receive frames in same time and differentfrequency, whereby the other base stations are aware of the schedulingin a neighboring base station in a way to reduce interference.
 9. Themethod of claim 2 further comprising constructing and refiningnon-overlapping regions and interference regions for each of the basestations and the plurality of terminals based on the periodicallydetermined relative locations of the plurality of terminals and the basestations.
 10. The method of claim 9 further comprising scheduling aresource of a base station of the base stations based on the constructedand refined non-overlapping regions and interference regions.
 11. Anapparatus for finding locations of base stations and using locationinformation of the base stations to increase frequency reuse in awireless network, the apparatus comprising: a scanning module configuredto scan a plurality of terminals on entry of the plurality of terminalsinto the wireless network by ways of transmitting digital signals to theplurality of terminals; an estimation module configured to estimaterespective distances from the plurality of terminals using thetransmitted digital signals; a transmission module configured totransmit distance information, by at least one of the plurality ofterminals, including the periodically estimated distances to each of thebase stations; a memory configured to store the distance information byeach of the base stations on in the memory and process the distanceinformation; a determination module configured to determine relativelocations of the plurality of terminals with respect to the basestations using the stored and processed distance information; and asteering module configured to steer antennas electronically based on thedetermined relative locations of the plurality of terminals and the basestations to increase frequency reuse by a scheduler interacting with theprocessor.
 12. The apparatus of claim 11, wherein determining relativelocations of the plurality of terminals with respect to the basestations includes cluster localizing, cluster transforming, and clusteroptimizing.
 13. The apparatus of claim 12, wherein the processor isconfigured to instruct the scheduler to schedule a resource to increasefrequency reuse.
 14. The apparatus of claim 12, wherein the processor isconfigured to construct and refine non-overlapping regions andinterference regions for each of the base stations and the plurality ofterminals based on the periodically determined relative locations of theplurality of terminals and the base stations.
 15. The apparatus of claim14, wherein the processor is configured to instruct the scheduler toschedule a resource based on the constructed and refined non-overlappingregions and interference regions.